The phony air raid: I see nothing! (Possible spoilers)
Possible spoilers ahead.
A modest issue with the phony air raid the Germans stage, during which Price stays behind to demonstrate to Schultz the "time bomb" Dunbar had made to blow up the ammunition train.
It seems to me a number of characters failed to notice some pretty obvious things.
First, Price pushes Harry and the Animal out the door, then shuts it and goes over to Schultz, by the chessboard. But is it really likely Harry and the Animal wouldn't have noticed that Price didn't leave with them and wasn't right behind them? Even making for the trenches, it seems probable they'd have noticed his absence, espcially since they'd just been talking to him.
Second, Price leaves with Schultz a minute or so later, after showing him the matchbook trick. Now, it's not likely any other prisoners would have seen the two leaving together, as they were in the air raid trenches and, presumably, couldn't see the barracks door. Still, wasn't it some risk to have the two men leave together? Could Schultz and Price have been certain no one would see them? More of a problem is what happened when Price went to the trenches himself, as he must have done. Again, wouldn't some of the prisoners have noticed his sudden, late arrival? Mightn't this made them a little suspicious of Price?
Third, Sefton stays behind in the barracks to spy on Schultz and Price. It's not really clear why Sefton should have done this: he had at this time no reason to be suspicious of Price himself, nor any reason to assume that the air raids were being used as cover for communications between the spy and the guards, hence no reason to stay behind. However, leave this (potentially substantial) question aside for the moment. How is it that Price and Schultz didn't see that Sefton hadn't left? They were keeping a pretty close eye on getting everyone out. But leave this aside too. When the two Germans leave, the camera pans over to Sefton, standing just one bunk away from the exit. Is it credible that neither Price nor Schultz wouldn't see him, that close? It was dark, but not that dark. They wouldn't have noticed movement or breathing or something? And Sefton tops it off by lighting a cigar after they leave. No one outside saw the lit match or burning cigar end? No one (prisoners or guards) ever noticed that Sefton hadn't left the barracks?
Nothing major here, it can be all explained away or fudged, even if the point is stretched a bit, but it does seem that a lot of people in Stalag 17 that night may have had their eyes wide shut, if I may bring in a rival picture.